Electronic transponder tuning procedure

ABSTRACT

A method is disclosed herein for tuning a responder unit (12). The method comprises the steps of storing energy in a responder unit energy accumulator (136) in a contactless fashion by RF energy transmitted from the interrogator unit (10) to the responder unit (12), and exciting within the responder unit (12) an RF carrier wave. The method further comprises the steps of transmitting the RF carrier wave in a first response from the responder unit (12) to the interrogator unit (10) and measuring within the interrogator unit (10) the received signal strength of the RF carrier wave of the first response. In further accordance with the invention tuning data may be transmitted to the responder unit (12) by sending at least one RF programming sequence from the interrogator unit (10) to the responder unit (12). The responder unit (12) upon receiving the RF programming sequence from the interrogator unit (10) would preferably modify an internally stored frequency setting within a memory (244) of the responder unit (12) in response to the first set of data. Other devices, systems and methods are also disclosed.

CROSS-REFERENCE TO RELATED PATENTS

The following coassigned patent applications are hereby incorporatedherein by reference: Ser. No. 07/981,635, pending.

FIELD OF THE INVENTION

This invention generally relates to a transponder arrangement comprisingan interrogator unit which transmits at least one RF interrogation pulseto a responder unit which thereupon sends data stored therein back tothe interrogator unit in the form of a modulated RF carrier. Theinterrogator unit of the present invention is further operable to derivetuning data from the responder unit and thereupon may initiateelectronic tuning of the responder unit's resonant frequency.

BACKGROUND OF THE INVENTION

There is a great need for devices or apparatuses which make it possibleto identify or detect as regards their presence at a predeterminedlocation objects which are provided with such devices or apparatuses incontactless manner and over a certain distance. An additional needexists to be able to change the resonant frequency with which suchdevices respond to such inquiries. An additional need exists to be ableto tune the resonant circuit of the responder unit to match that of theinterrogator unit, such as in the case the two units originally werematched in frequency and the resonant frequency of the responder unithas drifted or because of detuning due to environmental effects.

Heretofore, in this field, radio-frequency identification (RF-ID)transponders are permanently tuned to a resonant frequency at thefactory. Certain environmental considerations such as presence of apara-magnetic or dia-magnetic material which lowers the inductance of anantenna and tunes it to a higher frequency (e.g. if the transponder isclose to copper or aluminum). Other conditions might cause a change inthe resonant frequency such as the ambient temperature or aging of thecomponents. In the application of a small wireless transponder, it isdesirable for any post-factory tuning to not require bulkyelectro-mechanical components as mechanically-variable capacitors ormechanically-variable inductors.

SUMMARY OF THE INVENTION

The needs outlined in the background of the invention can be met withthe inventive concept disclosed hereinbelow. For universal usability ofsuch an arrangement the interrogation or enquiry unit is preferablyhandy and compact so that it withstands rough treatment in practice. Theresponder is preferably very small so that it can readily be attachedto, or inserted in, the objects to be detected.

The invention is based on the problem of providing a transponderarrangement with the aid of which the aforementioned requirements can befulfilled and with which the necessary responder device can be made veryeconomically and very small so that it can be used for a great varietyof purposes, in particular whenever many objects are to be provided withthe responder unit. The responder unit is to be constructed so that ithas a very low energy requirement and does not need its own power sourcewhich after a certain time would have to be renewed.

This problem is solved in the transponder arrangement, according to theinvention, by providing an energy accumulator within the responder unitby which the energy contained in the RF interrogation pulse is stored.The responder unit in the preferred embodiment provides means to detectthe termination of the reception of the RF interrogation pulse and thepresence of a predetermined energy amount in the energy accumulator,thereupon triggering the excitation of an RF carrier wave generatoroperating with the frequency contained in the RF interrogation pulse.Still further means are provided to demodulate, from the RF carrierwave, data which may be used to change or "tune" the frequency withwhich the RF carrier wave generator operates.

As such a method is disclosed for tuning a responder unit. The methodcomprises the steps of storing energy in a responder unit energyaccumulator in a contactless fashion by RF energy transmitted from saidinterrogator unit to said responder unit, and exciting within saidresponder unit an RF carrier wave. The method further comprises thesteps of transmitting said RF carrier wave in a first response from saidresponder unit to said interrogator unit and measuring within saidinterrogator unit the received signal strength of said RF carrier waveof said first response. In further accordance with the invention tuningdata may be transmitted to the responder unit by sending at least one RFprogramming sequence comprising a first set of data from saidinterrogator unit to said responder unit. The responder unit uponreceiving said RF programming sequence from said interrogator unit wouldpreferably modify an internally stored frequency setting within saidresponder unit in response to said first set of data.

In an embodiment of the invention a protocol is further provided formonitoring a first response from the responder unit and storing in amemory the strength of the first response. The protocol then providesthat the tuning information be sent to the responder unit, and that theresponder unit's response using the new frequency derived from thetuning information also be measured for strength of response. Amicroprocessor might successively perform this operation until a localmaximum is found.

Advantageous further developments and purposes will be appreciated byreference to the detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block circuit diagram of the interrogator unit according tothe invention;

FIGS. 2a-2b are graphs of the responder unit's response transmittedpower vs. frequency wherein the desired frequency is denoted as f₀ ;

FIG. 3 is a block circuit diagram of the responder unit according to theinvention;

FIG. 4 is a block diagram of an alternative system block diagram using aloosely coupled pick-up coil to detect the responder unit's responsetransmitted power; and

FIGS. 5a-5b are graphs illustrating the coupling of power between theresponder unit and interrogator unit for progressively closer matchedresponder unit tuned frequencies.

Corresponding numerals and symbols in the different figures refer tocorresponding parts unless otherwise indicated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, the interrogation unit 10 contains as centralcontrol unit a microprocessor 18 which is responsible for the control ofthe function sequences. A wireless datacom transceiver 19 under controlof microprocessor 18 is responsible for communications with otherinterrogator units having other wireless datacom transceivers and forcommunication with responder units 12 (not shown, see FIG. 3). Thewireless datacom transceiver 19 comprises an RF oscillator 20 whichgenerates RF oscillations as soon as it has been set in operation by asignal at the output 22 of the microprocessor 18. Further componentswhich are preferably contained within the wireless datacom transceiver19 include a modulator 24, an output amplifier 26, an antenna 33, aninput amplifier 52, and a demodulator 62. Although, preferably, thesecomponents are contained in the interrogator unit 12 it may not benecessary for all the components to be used. For example, in anotherembodiment of the invention the amplifiers 26,52 might not be needed. Insuch an instance the RF oscillator 20 might be constructed to directlyradiate into the transmitting medium without the use a separate antenna33.

Still referring to FIG. 1, the oscillations of RF oscillator 20 may bemodulated by a modulator 24 which is controlled by an output 34 of themicroprocessor 18. The output signal of the RF oscillator 20 is suppliedby an amplifier 26 to an antenna 33 which transmits the RF interrogationpulse supplied to it by the oscillator 20 and receives the RF signalsent back by the responder unit 12. The RF signals received by theantenna 33 are supplied to an amplifier 52 which amplifies the RFsignals. The output of the amplifier 52 is connected to a demodulator 62which from the signal supplied thereto generates a demodulated datastream which is supplied to the input 64 of the microprocessor 18. In apreferred embodiment, the demodulator circuitry 62 might further providea radio signal strength indictor (RSSI) signal which is an analog signalindicating the strength of the received signal. RSSI might be receivedby an analog-to-digital converter (ADC) 63 which would make a digitalsignal indicating the received signal strength available at the input 65of microprocessor 18. The use of this information will be describedhereinbelow.

In accordance with the present invention, the interrogator 12 is furtheroperable to measure the strength of a received communication signal,including the effects of coupling efficiency and other filtering of thereceived signal. One method of doing this is by the RSSI signaldiscussed above, although many other methods known in the art could beused. Power or amplitude measurements of the incoming signal are bothpossible ways to measure the effective communication signal strengthbetween responder unit 12 and interrogator unit 10. For example, if theinterrogator 10 is in wireless electrical communication with a responderunit 12, then the efficiency of this wireless communication should bemaximized when the resonant frequency of the responder's transmittingantenna 133 (not shown, see FIG. 3) is exactly matched to the resonanceof the interrogator's receiving antenna 33.

The importance of this frequency matching is illustrated in FIGS. 2a-b.Notice in FIG. 2a that the peak of transmission power of the responder'stransmitting antenna 133 is not aligned with the desired frequency f₀.The desired frequency f₀ is normally the resonant frequency of theinterrogator's receiving antenna 33. This frequency mismatch results inlowered signal coupling between the antennas 33,133. In the exampleshown, the power spectrum intersects with the desired frequency f₀ atapproximately 50% of its maximum, resulting in a great loss of rangeand/or immunity to interference. The radio signal strength indicator(RSSI) signal will be a measurement of the received signal strength asit is coupled between the transmitting and receiving antennas 133,33through the transmitting medium. As such, it will have a maximum whichgenerally occurs when the transmitting and receiving antennas 133,33 areidentically tuned. By using this RSSI signal, as converted by ADC 63,the interrogator unit 10 can tune the responder unit 12 by sending datato the responder unit 12 corresponding to a change or Δ (delta) infrequency. An example protocol for tuning the responder 12 might be tosend Δ₁ and Δ_(h) data to the responder unit 12, where Δ₁ has the effectof tuning the resonant circuit 130 of the responder unit 12 to a lowerfrequency than is effected by Δ_(h). The interrogator unit 10 thenmonitors the RSSI signal via ADC 63 as the responder unit 12 respondsusing both the Δ₁ and the Δ_(h) data to modify its resonant frequency aswill be described below. If the RSSI signal is greater using Δ₁ thanusing Δ_(h), then in this sample protocol one would assume that theresponder unit is detuned to a higher than desired frequency and that bylowering the resonant frequency by Δ₁ the tuning match betweentransmitter and receiver has been improved. In this instance, theresonant frequency would continue to be lowered in Δ₁ increments untilthe RSSI signal ceases to increase incrementally. At this time theprotocol might assume that a maximum has been reached and that theresponder unit has been properly tuned. Conversely, if the RSSI signalis greater using Δ_(h) than using Δ₁, then in this sample protocol onewould assume that the responder unit is detuned to a lower than desiredfrequency and that by increasing the resonant frequency by Δ_(h) thetuning match between transmitter and receiver has been improved. In thisinstance, the resonant frequency would continue to be increased in Δ_(h)increments until the RSSI signal ceases to increase incrementally. Atthis time the protocol might assume that a maximum has been reached andthat the responder unit has been properly tuned. Naturally, many otheralgorithms exist for finding local extrema, for example, adaptivealgorithms might not only record the direction of the change in the RSSIsignal, but also the magnitude. If the change in magnitude is small thenit might be desirable, depending on the characteristic shape of thefrequency response, to increase the magnitude of the Δ₁ or Δ_(h). Manysuch algorithms are well known in the art and will be apparent topersons skilled in the art upon reference to the description. It istherefore intended that the appended claims encompass any suchmodifications or embodiments. Without limiting the scope of theinvention, the procedure of programming a responder unit 12 with tuningdata will now be described below in reference to a half-duplexcommunication protocol. Other methods to program a responder unit 12will be apparent to one of ordinary skill in the art upon review of thisspecification. It is therefore intended that the appended claimsencompass any such modifications or embodiments.

The responder unit 12 illustrated in FIG. 3 contains for reception ofthe RF interrogation pulse a parallel resonant circuit 130 having a coil132 and a capacitor 134. In addition the parallel resonant circuit 130is connected to an RF bus 138. An RF carrier occurs at the RF bus 138whenever the parallel resonant circuit 130 receives an RF interrogationpulse from the interrogator unit 10. Control circuit 118 receives thisRF signal and in the preferred embodiment will respond to the RFinterrogation pulse after the interrogator unit 10 ceases transmitting.Control circuit 118 responds by furnishing at its output 188 anexcitation pulse or pluck signal. Said excitation pulse renders thefield-effect transistor 190 conductive which in turn applies the RF bus138 to ground for the duration of the excitation pulse. This provides adirect current from the storage capacitor 136 through the coil 132 thusproviding energy to the resonant circuit and maintaining a carrier waveoscillation in the resonant circuit 130.

Connected to the RF bus 138 is a capacitor 198 which by a field-effecttransistor (FET) 200 acting as a switch can be operatively connected tothe parallel resonant circuit 130. In this manner data can be modulatedupon the carrier wave. Specifically, if the FET 200 is non-conducting orswitched "off" then the carrier wave will continue to oscillate at itsnormal frequency. If, however, the FET 200 is made conductive orswitched "on" then the capacitor 198 will be connected in parallelacross the resonant circuit thereby providing a new resonant frequencywhich will be lowered by the added capacitance. In response to dataapplied to the gate of FET 200 the carrier wave is then frequencymodulated.

The control circuit 118 is further operable to demodulate, from the RFcarrier wave of the RF programming sequence, data which may be used tochange or "tune" the frequency with which the RF carrier wave generatoror resonant circuit 130 operates. For changing or tuning the resonantcircuit 130 frequency, a programmable tuning network 238 is provided inthe preferred embodiment of the present invention. This programmabletuning network 238 operates by switching a network of parallelcapacitors 240, each capacitor 240 being connected through afield-effect transistor or FET 242 in parallel with the resonant circuit130. Each field-effect transistor 242 is connected to a latch 244 whichreceives and latches data from the control circuit 118 via data bus 220.An EEPROM might replace the latch 244 to store the EEPROM resonancetuning function. The contents of the EEPROM can be changed by thecontrol circuit 118 in response to commands sent by the interrogatorunit 10. By switching a field-effect transistor 242 to a conducting "ON"state, its associated capacitor 240 is connected in parallel withparallel resonant circuit 130. This added capacitance will lower theresonant frequency of the parallel resonant circuit 130. By switching afield-effect transistor 242 to a non-conducting "OFF" state, itsassociated capacitor 240 is floating and has no effect on the parallelresonant circuit 130. A network 238 of FET/capacitor pairs 240,242 canprovide many different values of added capacitances depending on thecombinations of each capacitor's 240 relative value as is well known inthe art. Alternatively, latch 244 could be a one-time-programmable (OTP)memory such that the data is fixedly stored therein and the device maybe permanently programmed to set the value of programmable tuningnetwork 238.

For the embodiment described above the responder unit 12 must be in afixed position relative to the interrogator unit 10 in order to havepredictably reliable field strengths to use as the tuning criteria. Thealternative embodiment shown in FIG. 4 does not carry this requirement.This alternative embodiment comprises a coil 70 loosely coupled to theresponder unit 12. This coil 70 preferably is coiled about responderunit 12 to detect the RF responses given by the responder unit 12. Thecoil connects to the signal amplitude detector 68 which decodes thesignal amplitude or field strength of the RF responses and communicatesthe result as a "Return Signal" to the ADC 63 which again would make adigital signal indicating the received signal strength available formicroprocessor 18.

With reference now to FIGS. 5a-5b, graphs are shown for severaldifferent frequencies (a, b, and c) to which the responder unit 12 istuned. FIG. 5a shows the "Power Signal" and the "Return Signal" as theyvary with time for instances in which the antenna is tuned to one of thethree frequencies (a, b, or c). The corresponding graph of FIG. 5b givesa frequency spectrum of the coupling between the interrogator unit 10 tothe responder unit 12 for the three frequencies as seen by the pick-upcoil 70. Each progressively lower frequency is more closely matched tothe resonant frequency of the interrogator unit 10 causing a much higherand narrower frequency response as shown in FIG. 5b. As a way todetermine the coupling strength between the interrogator and responderunit 10,12 the interrogator unit 10 can measure the time in which ittakes for the "Power Signal" as measured by the pick-up coil to reach agiven level. The more quickly the "Power Signal" reaches this givenlevel, the more highly tuned the responder unit 10 is to theinterrogator unit 10.

Yet another method for retuning or initializing the responder unit afternormal RF-ID interrogation cycles is to measure the strength of RFresponses to consecutive reading cycles. In this case two or moreinterrogations can be executed where the interrogator unit 10 asks theresponder unit 12 to respond with a lower and a higher tuning capacitortrimming value. The interrogator unit 10 then analyzes theresponse/field strength and continues retuning or confirms the previousstatus.

A few preferred embodiments have been described in detail hereinabove.It is to be understood that the scope of the invention also comprehendsembodiments different from those described, yet within the scope of theclaims.

"Microcomputer" in some contexts is used to mean that microcomputerrequires a memory and "microprocessor" does not. The usage herein isthat these terms can also be synonymous and refer to equivalent things.The phrase "processing circuitry" or "control circuitry" comprehendsASICs (application specific integrated circuits), PAL (programmablearray logic), PLAs (programmable logic arrays), decoders, memories,non-software based processors, or other circuitry, or digital computersincluding microprocessors and microcomputers of any architecture, orcombinations thereof. Memory devices include SRAM (static random accessmemory), DRAM (dynamic random access memory), pseudo-static RAM,latches, EEPROM (electrically-erasable programmable read-only memory),EPROM (erasable programmable read-only memory), registers, or any othermemory device known in the art. Words of inclusion are to be interpretedas nonexhaustive in considering the scope of the invention.

Implementation is contemplated in discrete components or fullyintegrated circuits in silicon, gallium arsenide, or other electronicmaterials families, as well as in optical-based or othertechnology-based forms and embodiments. It should be understood thatvarious embodiments of the invention can employ or be embodied inhardware, software or microcoded firmware.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. For instance, in systems using a full duplex orsimultaneous power/receive protocol, the signal amplitude informationcan be derived from the modulated sidebands which are created by theresponder from the carrier emitted. It is therefore intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A method of communicating between an interrogatorunit having a first resonant circuit and a responder unit having asecond resonant circuit, said method comprising the steps of:a) storingenergy in a responder unit energy accumulator in a contactless fashionby RF energy transmitted from said interrogator unit to said responderunit; b) exciting within the resonant circuit of said responder unit anRF carrier wave; c) measuring the signal strength of said RF carrierwave; and d) adjusting the resonant frequency of one of said resonantcircuits responsive to said signal strength measurement.
 2. The methodof claim 1 wherein said signal strength of said RF carrier wave ismeasured by a pick-up coil which is loosely coupled to said secondresonant circuit of said responder unit.
 3. The method of claim 1 andfurther comprising the step of transmitting said RF carrier wave in afirst response from said responder unit to said interrogator unit. 4.The method of claim 3 and further comprising step of measuring withinsaid interrogator unit the received signal strength of said firstresponse.
 5. The method of claim 4 wherein the step of adjusting theresonant frequency of said one of said resonant circuits responsive tosaid signal strength measurement is by transmitting at least one RFprogramming sequence from said interrogator unit to said responder unit.6. The method of claim 5 and further comprising the step of receiving atsaid responder unit a first set of data transmitted by said RFprogramming sequence from said interrogator unit.
 7. The method of claim6 and further comprising the step of modifying an internally storedfrequency setting within said responder unit in response to said firstset of data.
 8. The method of claim 7 wherein said RF carrier wave isgenerated by a parallel LC oscillator having at least one parallelinductor and at least one parallel capacitor.
 9. The method of claim 8and further comprising the step of modifying the frequency of said RFcarrier wave in accordance with said internally stored frequency settingby selectively changing the capacitance of said LC oscillator.
 10. Themethod of claim 9 wherein said RF carrier wave is generated by aparallel LC oscillator having said at least one parallel inductor and atleast two parallel capacitors.
 11. The method of claim 9 wherein saidcapacitance of said LC oscillator is selectively changed by selectivelyconnecting and disconnecting one of said at least two parallelcapacitors by a switch.
 12. The method of claim 9 and further comprisingthe step of storing the received signal strength subsequent to saidmeasuring step.
 13. The method of claim 12 and further comprising thestep of sending a second set of data transmitted by another RFprogramming sequence from said interrogator unit.
 14. The method ofclaim 13 and further comprising the step of modifying the frequency ofsaid RF carrier wave in accordance with said second set of data byselectively changing the capacitance of said LC oscillator.
 15. Themethod of claim 14 and further comprising the step of transmitting saidRF carrier wave in a second response from said responder unit to saidinterrogator unit.
 16. The method of claim 15 and further comprising thestep of measuring within said interrogator unit the received signalstrength of said RF carrier wave of said second response.
 17. The methodof claim 16 and further comprising the step of comparing said storedreceived signal strength with said measured signal strength of saidsecond response.
 18. A method of communicating between an interrogatorunit having a first resonant circuit and a responder unit having asecond resonant circuit, said method comprising the steps of:a) storingenergy in a responder unit energy accumulator in a contactless fashionby RF energy transmitted from said interrogator unit to said responderunit; b) exciting within said responder unit an RF carrier wave; c)transmitting said RF carrier wave in a first response from saidresponder unit to said interrogator unit; d) measuring within saidinterrogator unit the signal strength of said first response; e)transmitting at least one RF programming sequence from said interrogatorunit to said responder unit; f) receiving at said responder unit a firstset of data transmitted by said RF programming sequence from saidinterrogator unit; and g) adjusting the resonant frequency of saidresponder unit resonant circuit responsive to said first set of data.19. A method of communicating between an interrogator unit having afirst resonant circuit and a responder unit having a second resonantcircuit, said method comprising the steps of:a) storing energy in aresponder unit energy accumulator in a contactless fashion by RF energytransmitted from said interrogator unit to said responder unit; b)exciting within said responder unit an RF carrier wave; c) transmittingsaid RF carrier wave in a first response from said responder unit tosaid interrogator unit; d) measuring within said interrogator unit thesignal strength of said first response; e) storing said measurement ofsaid first response signal strength; f) transmitting a RF programmingsequence from said interrogator unit to said responder unit; g)receiving at said responder unit a first set of data transmitted by saidRF programming sequence from said interrogator unit; h) adjusting theresonant frequency of said responder unit resonant circuit responsive tosaid first set of data; i) transmitting said RF carrier wave in a secondresponse from said responder unit to said interrogator unit; j)measuring within said interrogator unit the signal strength of saidsecond response; and k) comparing said stored first response measurementto said second response measurement.
 20. Transponder arrangementcomprising:a) an interrogator unit which transmits at least one RFprogramming sequence containing tuning data followed by at least one RFinterrogation pulse, said interrogator unit comprisingi) a transmitterwhich transmits said RF interrogation pulse and said RF programmingsequence, ii) a receiver for receiving a wireless response from aresponder unit, iii) a detection circuit for detecting the strength of acarrier wave generated by said responder unit, and iv) a control circuitfor analyzing the detected strength of said carrier wave and fordetermining if a new set of tuning data for another RF programmingsequence needs to be computed; and b) a responder unit which uponreceipt of said RF interrogation pulse transmits read data storedtherein back to the interrogator unit in the form of said wirelessresponse, said responder unit comprisingi) a responder unit receptioncircuit for receiving said tuning data transmitted by said RFprogramming sequence from said interrogator unit, ii) a memory suitablefor having memory data therein modified by said tuning data received bysaid reception circuit, iii) a responder unit energy accumulator whichstores energy contained in the RF interrogation pulse, iv) a responderunit RF carrier wave generator having a resonant frequency, and v) atuning circuit which modifies the resonant frequency of said RF carrierwave generator in accordance with said memory data.